Fix #506, update linux sysmon to use /proc/stat

[jphickey]

---

name: FSW Code Change
about: Flight Software code changes
labels: fsw

Description of Change

Use data from /proc/stat instead of /proc/schedstat. The latter was more intended for debugging the kernel and is not widely available, as it depends on kernel options to enable it.

The /proc/stat data should be universally available on Linux, but the format and units are somewhat different. This also enables us to segregate the CPU usage into user and kernel mode. The data comes for free with the idle info, so this makes it available as well.

Linked Issue

Closes #506

Requirements Impact

• Requirement ID(s):
• Requirements updated as necessary
• Existing requirements are still satisfied by this change

Testing Evidence

Execute CFS w/HS on Linux host. Verify that CPU load info is being correctly published by HS.
Note that without /proc/schedstat, the previous impl would fail to initialize.

Areas of Expertise Touched

• ASTRO
• CI/CD
• COSMOS
• Cybersecurity
• Docker
• EDS
• Git
• PSPs
• SBN
• SMP
• Tables
• TSN
• Unit Tests
• Other

---

Author Checklist

• Linked GitHub issue is referenced above
• Code has been formatted with .clang-format
• Static analysis workflows ran and passed
• Unit tests (UT Assert) updated/added to cover code changes
• Unit test workflows ran and passed
• COSMOS test suite was run; tests updated/added if relevant changes were made
• Requirements have been reviewed; updated or confirmed still satisfied (see above)
• Testing evidence is included above
• Self-review of the diff completed

---

Reviewer Checklist

• Code logic is correct and matches the stated intent
• Code is readable, maintainable, and follows project conventions (ask your lead if you are unsure of where to find these conventions)
• .clang-format has been applied
• Static analysis results reviewed and acceptable
• The change has been exercised by the unit tests (not just that tests pass — the new/changed code paths are actually covered)
• COSMOS test suite was executed against this change and results reviewed (or confirmed N/A with justification)
• Reviewer has independently verified the change behaves as described (e.g., by running the tests locally, reviewing CI output in detail, or performing additional ad-hoc testing as warranted)
• Memory safety reviewed (allocation, bounds, lifetime, stack usage)
• Requirements impact reviewed and appropriate
• Error handling is appropriate
• Appropriate Expert areas have been reviewed

Reviewer Testing Notes

[jphickey]

NOTE: the other warnings in the generic-vxworks-rtp module are fixed in #510. Those warnings can be ignored here. This fixes the other 2 warnings that were in linux-sysmon.

[jphickey]

Rebased since the other static analysis warning was fixed. This should get a clean run.

[chillfig]

Found a potential overbounds read if we have a large number of CPUs. Risk is low assuming number of CPUs are nominal.

[chillfig]

Could maybe use a clang-format (https://github.com/nasa/PSP/actions/runs/37805865884/job/113409851932?pr=509) but otherwise looks good to me!